Cold water on global warming plans

Many people will sympathise with the frustration exhibited by the UN development programme's Kevin Watkins (For all this talk, still we head steadfastly for catastrophe, September 26). It is true that "when adjusted for population, China's carbon footprint is less than one-fifth that of the US". But there are other ways of looking at this issue. Environmentalists, including the Ehrlichs and the Meadows in the US, have long been concerned about the need for humanity to live within natural limits.

If we apply this concept on a national basis, then we find that China's carbon footprint just undershoots its biocapacity, whereas the US just exceeds it. There is virtually nothing to choose between them on this benchmark. And that may well point to a means for securing agreement between these large carbon emitters on a post-2012 climate change regime. Perhaps a more hopeful scenario.Professor Geoffrey HammondDirector, International Centre for the Environment, University of Bath

Although Kevin Watkins is right in portraying our climate policies as being the equivalent of fiddling while Rome burns, he is wrong in his evaluation of the EU emissions trading scheme as being a "step in the right direction". The scheme helps industry delay the transition to clean technology and has transformed the challenge of climate change into a lucrative business opportunity for the biggest carbon criminals and a handful of brokers. The tough political decisions Watkins refers to involve ending subsidies on fossil fuels, penalising polluters and pouring money into renewables infrastructure, rather than the shell-game accountancy we have witnessed with carbon trading. Kevin SmithCarbon Trade Watch

There is a fundamental flaw in the idea that enhanced ocean mixing might provide a technological fix to counter global warming (How sea tubes could slow climate change, September 27). Deep, cold water is not only rich in nutrients but is also high in dissolved carbon dioxide, at a concentration that can be nearly twice as great as in the air. Bringing such water to the surface will, at least initially, have the opposite effect to that intended - releasing carbon dioxide and adding to the problem. It seems that neither James Lovelock, Chris Rapley or the editor of Nature checked this basic biogeochemistry before announcing their equivalent of a perpetual motion machine, that would anyway require a major energy investment (and carbon dioxide release) for its large-scale manufacture. Dr Phillip WilliamsonUK Surface Ocean-Lower Atmosphere Study, University of East Anglia